Method of rifling gun barrels



April 27, 1943. o. w. BONNAFE 2,317,514

Filed May 22, 1941 2r E-l l-SIE.

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Sheets-Sheet 2 Patented Apr. 27, 1943 METHOD oF RrFLnvG GUN BARRELs Oliver W. Bonnafe, Hudson, Mass., assignor to The Lapointe Machine Tool Company, Hudson, Mass., a corporation of Maine Application May 22, 1941, Serial No. 394,693

3 Claims.

This invention relates to nishing the barrels of ries or other types of guns in which shallow and slightly helical rifle grooves are provided to give the projectile a spinning or twisting motion as it leaves .the gun.

It is the general object of my present invention to provide an improved method of broaching such helical grooves in a gun barrel, and also to provide an improved and accurate method of reaming the gun barrel after the grooves are broached.

My invention further relates to certain ordered procedure which will be hereinafter described and more particularly pointed out in the appended claims.

Certain tools adapted for use in the practice of my improved method are shown in the drawings, in which Fig. 1 is a partial side elevation of a broach adapted for performing the first grooving operation by my improved method;

Figs. 2, 3, 4, and 5 are sectional end elevations, taken along the lines 2 2, 3 3, 4 4 and 5 5 respectively in Fig. 1;

Fig. 6 is a partial side elevation of a broach adapted for performing the second grooving operation;

Figs. 7, 8, 9 and 10 are sectional end elevations, taken along the lines 1 1, 8 8, 9 9 and Ill-l0 in Fig. 6 respectively;

Fig. 11 is a partial side elevation of a broach adapted for performing the third grooving operation;

Figs. l2, 13, 14 and 15 are sectional end elevations, taken along the lines I2 |2, |3-I3, M M and j 5 1 5 in Fig. 11 respectively;

Fig. 16 is a partial side elevation of a broach adapted for performing the fourth grooving operation;

Figs. 17, 18, 19 and 20 are sectional end elevations, taken along the lines Il l'l, l8-I8, I9 I9 and 20 2U in Fig. 16 respectively;

Fig. 21 is a partial side elevation of a broach adapted for performing the nal or reaming operation by my improved method;

Figs. 22, 23, 24 and 25 are sectional end elevations, taken along the lines 22 22, 23-23, 24 24 and 25-25 in Fig. 21 respectively;

Fig. 26 is a transverse sectional view of a gun barrel to be ried;

Fig. 27 is a transverse sectional view of the same barrel after it has been rifled by my improved method; and

Fig. 28 is a partial transverse sectional view showing the portions of stock removed by suc- CTI cessive operation of the tools shown in Figs. 1 to 25.

In order that .the advantages of my improved method may be more clearly understood, it may be stated briefly that the common method of riflng a gun barrel is to cut each groove separately by repeated passes of a single-tooth cutter therethrough. As a considerable number of grooves are required, which number increases with the diameter of the bore, the riiiing of a gun barrel by this heretofore common practice consumes a large amount of time and is correspondingly expensive. By my improved method, I produce a completely rified and reamed barrel by passing a limited number of broaches once only through the barrel to be ried. Each of these broaches operates simultaneously on all of the grooves to be formed in the barrel.

In Fig. 26 I have shown a transverse section of a gun barrel B to be grooved or rifled and for purposes of illustration have indicated that the barrel has an internal diameter of .296". In Fig. 27 I have shown a transverse section of the same barrel B after the barrel has been riiied and nished internally by my improved method. The reamed internal diameter is now .301" and the barrel has been provided with four grooves G which are equally spaced and which have an outside diameter of .310" between the bottoms of opposite grooves.

In Fig. 28 I have shown an enlarged transverse section in which the portions of stock removed by successive operations are indicated at a, b, c, d and e.

Brieiiy stated, relatively narrow grooves of partial depth are first produced by removing the portions a by the broach shown in Fig. 1, with either the broach or the work positively rotated to provide the correct twist or pitch. The grooves are then broached to substantially full depth but with each groove slightly reduced in width by removal of the portion indicated at b in Fig. 28 and by operation of the tool shown in Fig. 6.

The third tool shown in Fig. 11 then removes spaced portions c, thus Widening the groove to' substantially ful1 depth. Each groove is then indicated at e in Fig. 28. During this -reaming operation, the broach has a relative twisting or helical motion in the bore, so that any tool marks produced in reaming will be parallel to the rifle grooves.' rather than parallel to the longitudinal axis of the barrel.

The specific construction of the reaming broach per se, shown in Fig. 21, and the advantages thereof are fully described in the prior application of Wilrose J. Phaneuf, Serial No. 380,055 and are not specifically claimed herein.

Positive rotation of the tool or the work is necessary only during the initial broaching operation.

I will now describe in more detail the specific construction of each of the five broaches shown in detail inFlgs. 1 to 25 inclusive.

In Figs. 1 to 5, I have shown the construction of the rst broach, which is provided with a leading pilot section 40, a first cutter 4|, a plurality o! intermediate cutters not shown, a last cutter 42, and a following pilot section 43. 'I'he leading pilot section 40 is oi circular cross section, as shown in Fig. 2, and is slidable with slight clearance in the bore of the gun barrel which is to be ritled. Assuming the bore to be .296", as indicated in Fig. 26, the pilot 40 may have a diameter of .295".

The first cutter 4i is shown as having four equally spaced grooving projections. Each projection has a width of .100", and. the outside diameter of the projections is .297". Any desired number of intermediate cutters may be interposed between the first cutter 4l and the last cutter 42, which is shown as having an outside diameter of .303".

The following fpilot 43 is similar in section to the cutters but without cutting edges. The spiral ribs on the pilot are also of slightly less width and of slightly less outside diameter, as indicated in Fig. 5;

During the operation of the broach shown in Figs. 1 to 5, it will be understood, as previously stated, that either the broach or the work will be positively rotated to produce the desired twist or pitch for the rifle grooves, which pitch must of course correspond to the pitch of the teeth on the cutters and to the pitch of the ribs on the following pilot section 43. All of the broaches except the ilrst are provided with spirally ribbed leading pilots and these broaches will follow the pitch established in the first operation without positive rotation of either broach or work.

The broach for the second operation is shown in Figs. 6 to 10, said broach comprising a leading pilot portion '50, a ilrst cutter 5I, intermediate cutters not shown, a last cutter 52, and a following pilot 53. The leading pilot 50 corresponds in construction and dimensions to the following pilot 43 of the first broach.

It will be noted that the width of the projections on the cutters 5I to 52 is slightly reduced to .095 while the outside diameter is gradually increased to .309". The ribs of the following pilot portion 53 are slightly reduced in width to .090" and the outside diameter to .308" for clearance.

The third broach, shown in Figs. 11 to 15 respectively, comprises a leading pilot portion 60 with a ilrst cutter 8|, intermediate cutters not shown, a iinal cutter 62, and a following pilot 63. the construction being identical with that shown in Fig. 6 exceptfor variations in dimensions as shown in Figs. 12 to 15. 'Ihe projections in the cutters 6I to 62 are increased to .150" in width asians and to an outside diameter in the last cutter l2 The fourth cutter, shown in Figs. 18 to 20, is similar to the second and third cutters and comprises a leading pilot portion 10, iirst cutter 1I, intermediate cutters not shown, last cutter 'I2 and following pilot 13. The cutter projections on the fourth broach are increased to a ilnal width of .175 and are gradually increased to a iinal31 outside diameter in the last cutter 12 of 0".

The iinal broach shown in Figs. 21 to 25 has a leading pilot portion 88, a nrst cutter 8 l a middle pilot portion 82, a last cutter 83, and a following pilot portion 84, together with intermediate cutters not shown. 'I'his iinal broach is used for reaming the bore of the barrel. The broach is centered by the ribs on the pilots, which have an outside diameter of .309", so that they are a close sliding t in the broached grooves which have a'n outside diameter of .310. All of the cutters in this fifth broach are of circular cross section and ream the bore of the barrel to a final and desired diameter of .301".

As previously explained, the reaming broach shown in Fig. 21 is guided in a helical path corresponding to the pitch ot the riile grooves, so that any tool marks produced by the cutters 8| to I3 are parallel to the riile grooves and thus do not retard the flight of the projectile, as might be the case if the tool marks were parallel to the longitudinal axis and at an angle to the riiie grooves.

Reference to Fig. 28 will indicate that the portions of stock to be removed by the different broaches are carefully distributed and approximately equal in cross sectional area, so that each broach performs substantially the same amount of work and may be operated at the same speed.

By the use of a set of breaches as herein described, and by following the procedure outlined, a gun barrel can be provided with a set of riiie grooves in much less time than has been previously necessary and with superior accuracy.

It will be understood that the dimensions shown in the drawings are illustrative only and may be varied to suit the size and material of the barrels to be ried. It will also be understood that the number of successive tools used in the production of ilnished rifle grooves may be increased or decreased also in accordance with the size or the material of the barrels. The number of grooves may also be varied.

For convenience, the signicant dimensions of the operative portions of the tools shown in the drawings are assembled in the following table but, as previously stated, these dimensions are illustrative only.

First pilot Flrstcutter Last cutter Last pilot 0D Width 0D Width 0D Width 0D width mmol .-.295 Rd .291 .10o 2ndtoo1 a02 .095 .3035 .095 .3 1132 g 'm 3rd 1 .09o .29s .15o .aoc .om .aos 1145 nmol .145 .29s .115 .31o .175 .mo .16o sthtooi .soo .16o .291 Rd .301 Rd .309 .16o

ments of material from all of said grooves by a series of broaching operations, and thereafter finishing the bore of said gun by passing an annular broach therethrough which is relatively guided in a helical path concentric with said rifle grooves and of the same twist as said grooves.

2. The method of riing gun barrels which comprises simultaneously broaching a plurality of initial helical grooves in a gun barrel, increasing both the depth and the width of said grooves by successive broaching operations, each performed on all of said grooves simultaneously, and thereafter finishing the bore of said gun by passing an annular broach therethrough which is relatively guided in a helical path concentric with said rifle grooves and of the same twist as said grooves.

3. The method of rifling gun barrels which comprises simultaneously breaching a plurality of initial helical grooves in a gun barrel, increasing both the depth and the width of said grooves by successive broaching operations, each performed on all of said grooves simultaneously and each removing approximately equal increments of material from said grooves, and thereafter finishing the bore of said gun by passing an annular broach therethrough which is guided in a helical path by and concentric with said rie grooves.

OLIVER W. BONNAFE. 

